Traditional telephony networks such as public switched telephone network (PSTN) employ Time Division Multiplex (TDM) circuits, copper cable pairs, and electronic switches to provide voice communication services. The PSTN uses a circuit-switched architecture in which a direct connection, or circuit, is made between two users. The circuit provides a full-duplex, or bi-directional, connection with extremely low latency, or delay, between the two end points. The connection is generally a logical connection through many switches and across a variety of wiring types (twisted-pair, fiber-optic cable, etc.). The users have exclusive and full use of the circuit until the connection is released. This circuit switching technology has slowly evolved over the last 100 years providing a complex mixture of analog and digital circuits with a variety of signaling techniques. Along the way, many different testing methods and monitor systems are developed to assist with the delivery of PSTN telephony signals.
Data communication, on the other hand, uses packet switching transmission technology. Data is assembled into distinct digital “packets” with addresses that are read by switches or routers as the packets are received. The switches/routers forward the packets onto the appropriate destination. Unlike the PSTN technology, there is no dedicated circuit connection between a sending station and a receiving station. As such, data packets from the sending station may take different routes to the same receiving station, depending on network traffic conditions and other factors. This type of transmission is only half-duplex, or unidirectional, which can easily lead to high delays between sending and receiving.
Internet Protocol (IP) provides a connectionless service, tracks Internet addresses of nodes, routes outgoing messages and recognizes incoming messages. In other words, IP provides the addressing needed to enable routers to forward data packets across multiple networks. Due to IP's inherent transmission efficiency of packet switching and IP's ability to run over any network medium (Ethernet, FDDI, ATM, Frame Relay, etc.), circuit switched networks (voice) and packet switched networks (data) are rapidly converging into one network, referred to as a Next Generation Telephony Network (NGTN).
Unlike the existing PSTN network, the new NGTN network is relatively immature and lacks sufficient testing and monitoring capabilities. Telephone service providers such as Competitive Local Exchange Carriers (CLECs), Regional Bell Operating Companies (RBOCs) and Inter-Exchange Carriers (IXCs) that want to take advantage of the IP technology are finding that Customer Premise Equipment (CPE) does not always adhere to established standards. This often makes the transition to the IP technology difficult, as the service providers may need to perform time-consuming manual pre-service tests in order to verify a subscriber's CPE configuration and existing or potential inter-operability problems.